Method and apparatus for wavelength selective switch
Apparatus and method embodiments are provided for implementing a wavelength selective switch (WSS). The embodiments use combinations of switchable polarization grating (SPG) and LC cells and combinations of polymer polarization grating (PPG) and LC cells to achieve 1×N WSS systems. An embodiment optical switch includes a liquid crystal cell and a polymer polarization grating (PPG) cell adjacent to the liquid crystal cell. The PPG includes a glass substrate, a photo-alignment layer overlying the glass substrate and comprising photosensitive polymer that has been physically altered by exposure using two interfering light beams with opposite handedness of circular polarization, and a polymerized liquid crystal layer overlying the photo-alignment layer on an opposite side of the glass substrate, the polymerized liquid crystal layer has been physically altered by illumination using a uniform light beam.
1. An optical switch comprising:
a liquid crystal cell; and
a polymer polarization grating (PPG) cell adjacent to the liquid crystal cell, the PPG comprising:
a glass substrate;
a photo-alignment layer overlying the glass substrate; and
a polymerized liquid crystal layer overlying the photo-alignment layer on an opposite side of the glass substrate, wherein the photo-alignment layer comprises photosensitive polymer that has been physically altered by exposure using two interfering light beams with opposite handedness of circular polarization.
2. The optical switch of claim 1 , wherein the polymerized liquid crystal layer has been physically altered by illumination using a uniform light beam.
3. The optical switch of claim 1 , further comprising:
a variable optical attenuator (VOA) comprising a second liquid crystal cell and a polarizer;
a prism or mirror positioned next to the PPG cell on an opposite side of the liquid crystal cell; and
one or more pairs of an additional liquid crystal cell and an additional corresponding PPG cell positioned between the PPG cell and the prism or mirror.
4. The optical switch of claim 3 , wherein the optical switch is a 1×2 N optical switch configured to optically connect one common port to 2 N separate ports, where N is a number of pairs of liquid crystal cells and corresponding PPG cells in the optical switch.
5. The optical switch of claim 1 , wherein both the liquid crystal cell and the PPG cell comprise a plurality of pixels corresponding to wavelength channels and aligned perpendicular to a direction of a plurality of parallel light beam paths through the optical switch corresponding to optical switch ports.
6. The optical switch of claim 5 , wherein the optical switch is designed to have equal distance between parallel output light beams from the optical switch.
7. The optical switch of claim 1 , further comprising:
a fiber array that transmits and receives one or more incident light beams to and from the liquid crystal cell and the PPG cell;
a micro lens array positioned on the optical path next to the fiber array;
a beam displacer positioned on the optical path next to the micro lens array;
a half wave plate array positioned on the optical path next to the beam displacer;
a cylindrical lens positioned on the optical path between the half wave plate array and the liquid crystal cell with the PPG cell;
a cylindrical reflection mirror facing the liquid crystal cell and the PPG cell behind the cylindrical lens on the optical path and positioned to reflect a light beam that is passed through the cylindrical lens back through the cylindrical lens; and
a grating facing the cylindrical reflection mirror behind the cylindrical lens on the optical path and positioned to diffract a light beam that is passed through the cylindrical lens back onto the cylindrical lens.
8. The optical switch of claim 1 , wherein the liquid crystal cell is configured to, with no applied voltage or a first applied voltage across the liquid crystal cell, pass an incident light beam that has a circular polarization to the PPG cell after reversing the circular polarization's handedness.
9. The optical switch of claim 8 , wherein the liquid crystal cell is configured to, with a second applied voltage across the liquid crystal cell, pass the incident light beam without changing the circular polarization's handedness.